Inspection method for inspecting electric characteristics of devices formed on target object

ABSTRACT

An inspection method for inspecting electric characteristics of devices formed on a target object using an apparatus including a vertical drive mechanism for lifting and lowering a movable mounting table and a control unit for controlling the vertical drive mechanism. The vertical drive mechanism includes an elevation shaft connected to the mounting table and a servo motor for driving the elevation shaft to lift and lower the mounting table. The control unit has a servo driver including a position control part for controlling a position of the motor, a torque control part for controlling a torque of the motor as a probe card is expanded or contracted by a change in temperature and a switching part for switching the position control part and the torque control part. The method includes heating or cooling the target object, controlling a position of the motor, and controlling a torque of the motor.

CROSS-REFERENCE(S) TO RELATED APPLICATIONS

This application is a continuation application of pending U.S.application Ser. No. 12/146,081, filed on Jun. 25, 2008, which claimspriority to Japanese Patent Application No. 2007-227182, filed on Aug.31, 2007.

FIELD OF THE INVENTION

The present invention relates to an inspection apparatus and aninspection method; and, more particularly, to an inspection apparatusand an inspection method capable of shortening an inspection time.

BACKGROUND OF THE INVENTION

A conventional inspection apparatus includes, e.g., a mounting table formounting thereon a target object (e.g., a wafer) to be inspected, themounting table having therein a temperature controller for controllingthe temperature of the wafer, a vertical drive mechanism for moving themounting table up and down, an XY table for moving the mounting tableand the vertical drive mechanism in X and Y directions, a probe cardarranged above the mounting table, and an alignment mechanism foraccurately aligning a plurality of probes of the probe card with aplurality of electrode pads of the target object placed on the mountingtable. The temperature of the wafer placed on the mounting table iscontrolled to a predetermined value by the temperature controller. Aspecified device formed on the wafer is brought into electrical contactwith the probes of the probe card through the alignment mechanism. Then,the probe card is overdriven by a prescribed overdrive amount so thatthe electric characteristics of the device can be inspected under apredetermined contact load.

In some cases, the inspection apparatus performs a high temperatureinspection by heating the wafer to a high temperature of, e.g., 100° C.or more. In other cases, the inspection apparatus carries out a lowtemperature inspection by cooling the wafer to a temperature of, e.g.,minus several tens of degrees centigrade. When performing the hightemperature inspection or the low temperature inspection, the targetobject is heated or cooled to a predetermined inspection temperature bythe temperature controller provided in the mounting table. Whilecontrolling the position of the mounting table with the vertical drivemechanism, the device and the probes are brought into contact with eachother under a specified contact load. The high temperature inspection orthe low temperature inspection is performed in this state. The verticaldrive mechanism includes, e.g., a ball screw connected to the mountingtable and a stepping motor for rotating the ball screw. The steppingmotor controls the amount of rotation of the ball screw and, eventually,controls the vertical position of the mounting table with increasedaccuracy.

In case of performing, e.g., the high temperature inspection of thewafer, the wafer placed on the mounting table is heated to, e.g., 100°C. or more, by use of the temperature controller provided in themounting table. The wafer placed on the mounting table is aligned withthe probes of the probe card by means of the alignment mechanism. In astate that the wafer and the probes are in contact with each other underthe predetermined contact load, the electric characteristics of thewafer are inspected at a high temperature of 100° C. or more.

In an initial stage of the inspection, however, the probe card is notyet heated while the wafer is already heated to a temperature of 100° C.or more by the temperature controller. Thus, there exists a greattemperature difference between the wafer and the probe card. For thisreason, if the wafer is overdriven by a predetermined amount to bringthe probes into contact with a first device of the wafer when inspectingthe latter, the probe card is heated and gradually expanded by the heatradiated from the wafer during the contact. Therefore, the device andthe probes make contact with each other under a load greater than thepredetermined contact load, which may possibly cause damage to thedevice or the probes.

In view of this, the high temperature inspection is performed afterpreheating and completely heat-expanding the probe card. As the probecard becomes greater in size, however, it takes a long time, e.g., 20 to30 minutes, to preheat the probe card. For example, Japanese PatentLaid-open Publication No. 2007-088203 (JP2007-088203A) discloses atechnique of shortening a preheating time of the probe card by makingthe probes of the probe card brought into direct contact with a waferheated to a predetermined temperature and preheating the probe card nearthe wafer.

In the technique disclosed in JP2007-088203A, however, a preheating timeis still required in addition to an actual inspection time. Therefore,there is a limit in shortening the total inspection time. Furthermore,if the wafer is moved away from the probe card during index movement ofa target object, the probe card is cooled to thereby change the heightof the tips of the probes. For this reason, the contact load is changedeach time when the index movement is carried out. In this case, however,it is impossible to control the contact load. Meanwhile, when performinga low temperature inspection of the wafer, there is a need to cool theprobe card to a temperature near the wafer temperature.

SUMMARY OF THE INVENTION

In view of the foregoing, the present invention provides an inspectionapparatus and an inspection method capable of shortening an inspectiontime by inspecting a target object without preliminarily heating orcooling a probe card during high temperature inspection or lowtemperature inspection, and also capable of performing the inspectionwith increased reliability by positively preventing damage of the probecard and the target object.

In accordance with an aspect of the present invention, there is providedan inspection apparatus for inspecting electric characteristics of aplurality of devices formed on a target object, the apparatus including:a movable mounting table having therein a temperature controller; avertical drive mechanism for lifting and lowering the mounting table; acontrol unit for controlling the vertical drive mechanism; and a probecard having a plurality of probes arranged above the mounting table, thetarget object being heated or cooled to a specified temperature by meansof the temperature controller and being inspected while the devices andthe probes of the probe card are brought into contact with each otherunder a predetermined contact load by means of the vertical drivemechanism, wherein the vertical drive mechanism comprises an elevationshaft connected to the mounting table and a servo motor for driving theelevation shaft to lift and lower the mounting table, wherein thecontrol unit comprises a servo driver which includes a position controlpart for controlling a position of the servo motor, a torque controlpart for controlling a torque of the servo motor as the probe card isexpanded or contracted by a change in temperature and a switching partfor switching the position control part and the torque control part.

Preferably, the servo driver is connected to a master computer formonitoring the inspection apparatus, and the master computer includes aposition command part for transmitting a position command signal to theposition control part, a torque command part for transmitting a torquecommand signal to the torque control part and a switching command partfor transmitting a switching command signal to the switching part basedon the torque of the servo motor.

The servo driver may further include a storage part for storing a torquevalue indicative of a contact load available each time when the electriccharacteristics of the devices are inspected.

In this case, the storage part may store upper and lower limit values ofthe predetermined contact load.

Preferably, the torque control part controls a contact load of thedevices and the probes in keeping with thermal expansion or contractionof the probe card to become equal to the predetermined contact load.

In this case, the torque control part may stop the servo motor when acontact load of the devices and the probes falls outside a range betweenthe upper and lower limit values.

In accordance with another aspect of the present invention, there isprovided an inspection method for inspecting electric characteristics ofa plurality of devices formed on a target object by using an inspectionapparatus which comprises a movable mounting table having therein atemperature controller; a vertical drive mechanism for lifting andlowering the mounting table; a control unit for controlling the verticaldrive mechanism; and a probe card having a plurality of probes arrangedabove the mounting table, the vertical drive mechanism including anelevation shaft connected to the mounting table and a servo motor fordriving the elevation shaft to lift and lower the mounting table, theinspection method comprising: a first step of heating or cooling thetarget object to a predetermined temperature; a second step ofcontrolling a position of the servo motor until the target object andthe probes come into contact with each other; and a third step ofcontrolling a torque of the servo motor after the target object and theprobes has come into contact with each other.

The inspection method may further comprise a step of storing a torquevalue indicative of a contact load available each time when the electriccharacteristics of the devices are inspected.

In the third step, a contact load of the devices and the probes may becontrolled in keeping with thermal deformation of the probe card tobecome equal to a predetermined contact load.

In the third step, a contact load of the devices and the probes may becontrolled to fall within a range between upper and lower limit valuesof a predetermined contact load.

In the third step, the servo motor may be stopped when a contact load ofthe devices and the probes falls outside a range between upper and lowerlimit values of a predetermined contact load.

In accordance with the present invention, it is possible to provide aninspection apparatus and an inspection method capable of shortening aninspection time by inspecting a target object without preliminarilyheating or cooling a probe card during high temperature inspection orlow temperature inspection, and also capable of performing theinspection with increased reliability by positively preventing damage ofthe probe card and the target object.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the present invention will become apparentfrom the following description of embodiments given in conjunction withthe accompanying drawings, in which:

FIG. 1 is a view for explaining major parts of an inspection apparatusin accordance with an embodiment of the present invention;

FIG. 2 is a flowchart illustrating an inspection method of the presentinvention performed by the inspection apparatus shown in FIG. 1; and

FIGS. 3A and 3B are views for explaining the inspection methodillustrated in FIG. 2.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, an embodiment of the present invention will be describedwith reference FIGS. 1 to 3.

First, an inspection apparatus of the present embodiment will bedescribed with reference to FIG. 1. As shown in FIG. 1, the inspectionapparatus 10 of the present embodiment includes, e.g., a mounting table11 for mounting thereon a target object (e.g., a wafer) W, the mountingtable 11 having therein a temperature controller, a vertical drivemechanism 12 for raising and lowering the mounting table 11, an XY table(not shown) on which the mounting table 11 and the vertical drivemechanism 12 are arranged, a probe card 13 arranged above the mountingtable 11 and provided with a plurality of probes 13A and an alignmentmechanism (not shown) for aligning the wafer W mounted on the mountingtable 11 with the probes 13A of the probe card 13. In a high temperatureinspection for example, the vertical drive mechanism 12 is designed tochange the current position of the mounting table 11 in response to thethermal expansion of the probe card 13, thereby keeping a predeterminedcontact load at all times so that the inspection can be performed in astable manner.

In case of performing the high temperature inspection of the wafer W,the wafer W placed on the mounting table 11 is heated to a temperatureof, e.g., 100° C. or more by means of the temperature controller. Whilethe mounting table 11 is moved in X and Y directions, the wafer W placedon the mounting table 11 is aligned with the probes 13A by the alignmentmechanism. After the wafer W is index-moved by the XY table, thevertical drive mechanism 12 brings one of a plurality of devices formedin the wafer W into electrical contact with the probes 13A under apredetermined contact load. Then, the electric characteristics of eachof the devices are inspected at a specified high temperature.

As can be seen in FIG. 1, the vertical drive mechanism 12 includes aball screw 14 connected to and suspended from the center of a lowersurface of the mounting table 11, a servo motor 15 for rotating the ballscrew 14, the servo motor 15 having an encoder 15A, and a servo driver16 for controlling the operation of the servo motor 15. The servo motor15 is position-controlled or torque-controlled by the servo driver 16. Anut member 14A is threadedly coupled to the ball screw 14 and a pulley15B is attached to the servo motor 15. A power transmission belt 17 iswound around the nut member 14A and the pulley 15. The torque of theservo motor 15 is transferred to the ball screw 14 via the pulley 15A,the power transmission belt 17 and the nut member 14A so that themounting table 11 can be moved up and down.

Use of the servo motor 15 and the servo driver 16 in the vertical drivemechanism 12 ensures that, even if the probe card 13 is thermallyexpanded, the servo driver 16 controls the position of the servo motor15 in a below-described manner until the wafer W and the probes 13A comeinto contact with each other. Thus, the servo driver 16 controls themounting table 11 with increased accuracy so that the wafer W placed onthe mounting table 11 can make electric contact with the probes 13A.After the mounting table 11 is overdriven to assure electric contactbetween the wafer W and the probes 13A, the position control of theservo motor 15 is switched to the torque control. Then, the servo driver16 controls the torque of the servo motor 15 with increased accuracy sothat the contact load between the wafer W and the probes 13A becomesequal to a predetermined contact load.

More specifically, the servo driver 16 is connected to a master computer20 through a network as shown in FIG. 1 and is operated by various kindsof command signals issuing from the computer 20. The servo driver 16includes a position control part 161 for controlling the position of theservo motor 15 in response to the command signals issuing from themaster computer 20, a torque control part 162 for controlling the torqueof the servo motor 15 in response to the command signals issuing fromthe master computer 20, and a switching part 163 for switching theposition control part 161 and the torque control part 162 in response tothe command signals issuing from the master computer 20. The servodriver 16 is designed to control the position or torque of the servomotor 15.

As shown in FIG. 1, the master computer 20 includes a position commandpart 21 for transmitting a position command signal P to the positioncontrol part 161, a torque command part 22 for transmitting a torquecommand signal T1 to the torque control part 162, a switching commandpart 23 for transmitting a switching command signal C to the switchingpart 163, and a monitoring part 24 for monitoring the mounting table 11through the servo motor 15. Even when the probe card 13 is thermallyexpanded during the high temperature inspection, the monitoring part 24monitors the mounting table 11 with reference to a feedback signal F ora torque signal T2 issuing from the servo motor 15. Based on themonitoring results, the position command signal P, the torque commandsignal T1 or the switching command signal C is transmitted to the servodriver 16. Thus, one of the devices of the wafer W placed on themounting table 11 is made to contact with the probes 13A under apredetermined contact load so that the high temperature inspection canbe performed with increased reliability. Furthermore, the monitoringpart 24 monitors the whole inspection process of the wafer W performedin the inspection apparatus 10 and transmits the switching commandsignal C to the servo driver 16 each time when the inspection of eachdevice of the wafer W is completed. In addition, the master computer 20is also connected to servo drivers of other inspection apparatuses tomonitor the latter.

As shown in FIG. 1, the position control part 161 includes a comparator161A for comparing the position command signal P transmitted from themaster computer 20 with the feedback signal F supplied from the encoder15A to generate a digital deviation signal, a D/A converter 161B forconverting the digital deviation signal generated in the comparator 161Ato an analog signal, and an amplifier 161C for amplifying an electriccurrent supplied from the D/A converter 161B. The position control part161 is designed to rotatingly drive the servo motor 15 based on anoutput current I fed from the amplifier 161C.

As can be seen in FIG. 1, the torque control part 162 includes acomparator 162A for comparing the torque command signal T1 issuing fromthe master computer 20 with the current value (the torque signal) T2supplied from the servo motor 15 to generate a digital deviation signal,a D/A converter 162B for converting the digital deviation signalgenerated in the comparator 162A to an analog signal, and an amplifier162C for amplifying the analog signal supplied from the D/A converter162B. The torque control part 162 is designed to control the torque ofthe servo motor 15 based on a torque signal (an electric current) T fedfrom the amplifier 162C. The torque control part 162 further includes astorage part 162D for storing, as a torque value, the contact loadavailable in the previous high temperature inspection and the tolerancevalues (the upper and lower limit values) of the contact load. Thetorque value stored in the storage part 162D is set as a contact loadwhen the next device is subjected to the high temperature inspection.Furthermore, the torque value is controlled to fall within a permissibletorque range between an upper and a lower limit value available duringthe high temperature inspection. The torque control part 162 is designedto stop the inspection in the event that the torque value falls outsidethe permissible torque range for any reason.

As shown in FIG. 1, the switching part 163 is operated in response tothe switching command signal C issuing from the master computer 20 andis designed to alternately switch the position control part 161 and thetorque control part 162. For example, the servo motor 15 lifts up themounting table 11 with a constant torque under the control of theposition control part 161 to thereby bring the wafer W placed on themounting table 11 into contact with the probes 13A, and the torque ischanged if the mounting table 11 is overdriven thereafter. At this time,the monitoring part 24 of the master computer 20 is monitoring thetorque signal T2. If the torque signal T2 is changed due to theoverdrive of the mounting table 11, a switching command signal istransmitted from the switching command part 23 to the switching part163. Consequently, the position control part 161 is switched to thetorque control part 162 which in turn controls the torque of the servomotor 15. In a conventional case, the probe card 13 is thermallyexpanded and the tips of the probes 13A are pressed against thecorresponding device. As a result, the contact load exceeds apredetermined value, which may possibly cause damage to the device orthe probes.

In the present embodiment, however, the servo motor 15 is switched fromthe position control to the torque control and is reversely rotated alittle bit to slightly reduce the torque, whereby the torque iscontrolled to become a torque value corresponding to the predeterminedcontact load. Once the high temperature inspection is completed underthe predetermined contact load, the master computer 20 performs indexmovement of the wafer W in response to the signals supplied from theinspection apparatus 10 and then transmits a switching command signal Cto the servo driver 16 to switch the torque control to the positioncontrol. Subsequently, the next device is subjected to the hightemperature inspection.

Next, an inspection method using the inspection apparatus 10 of thepresent embodiment will be described with reference to FIGS. 1 to 3.

If the wafer W is mounted on the mounting table 11 in a conventionalmanner, the wafer W is heated to a high temperature of 100° C. or moreby means of the temperature controller. During this, the mounting table11 is moved in the X and Y directions and the wafer W is aligned withthe probes 13A of the probe card 13 by means of the alignment mechanism.After the alignment is completed, the mounting table 11 is moved in theX and Y directions so that the device to be inspected first arrives justbelow the probes 13A.

Once the first device of the wafer W arrives just below the probes 13A,the master computer 20 transmits a position command signal P to theposition control part 161 of the servo driver 16. Then, as illustratedin FIG. 2, the servo driver 16 begins to control the position of theservo motor 15 (step S1). In the position control part 161, thecomparator 161A receives the position command signal P from the mastercomputer 20 and also receives the feedback signal F from the encoder 15Aof the servo motor 15. Then, the comparator 161A transmits a deviationsignal indicative of the deviation between the position command signal Pand the feedback signal F to the D/A converter 161B. The D/A converter161B converts the deviation signal to an analog signal and transmits theanalog signal to the amplifier 161C. The amplifier 161C amplifies theelectric current received from the D/A converter 161B and applies theamplified current to the servo motor 15, thus lifting up the mountingtable 11. As the mounting table 11 is lifted up and the wafer W is movedtoward the probe card 13, the probe card 13 is gradually heated andthermally expanded by the heat radiated from the mounting table 11.Then, the mounting table 11 is overdriven to bring the wafer W and theprobes 13A into electrically conducting contact with each other (stepS2).

The probes 13A are directly heated by the wafer W due to the contactbetween the probes 13A and the wafer W. Also, the probe card 13 isgradually heated by the heat radiated from the mounting table 11,thereby causing heat expansion of the probe card 13 as a whole. As aresult, as indicated by a dashed dotted line in FIG. 3A, the height ofelectric contact between the electrode pads Dp of the device D and theprobes 13A becomes lower than an original contact height. Therefore, theprobes 13A are pushed up to the position indicated by a solid line inFIG. 3A. Consequently, the electrode pads Dp and the probes 13A comeinto contact with each other under a contact load greater than thepredetermined contact load.

In the present embodiment, as illustrated in FIG. 2, the master computer20 monitors the torque generated in the servo motor 15 by the overdrive(step S3) and stores the current torque T2 of the servo motor 15 in thestorage part 162D of the servo driver 16 (step S4) as shown in FIG. 1.At the same time, the master computer 20 transmits a switching commandsignal C to the switching part 163 of the servo driver 16 and allows theswitching part 163 to switch the position control part 161 to the torquecontrol part 162 (step S5) so that the torque control part 162 canperform torque control.

In the servo driver 16, the comparator 162A compares the current torquesignal T2 supplied from the servo motor 15 with the torque signaltransmitted from the storage part 162D to determine whether or not thereis a change in torque due to a difference between both signals (stepS6). If the torque is changed, a deviation signal indicative of the sameis transmitted to the amplifier 162C to control the torque of the servomotor 15. Then, the servo driver 16 rotates the ball screw 14 in thereverse direction so that the torque of the servo motor 15 can bereduced to the predetermined torque. Thus, the probes 13A are loweredfrom the position indicated by a dashed dotted line in FIG. 3B to theposition indicated by a solid line (step S7). In this state, the hightemperature inspection of the device D is performed under thepredetermined contact load. The torque value of the servo motor 15available at this time is registered and stored in the storage part162D. The torque value thus registered is used in the second deviceinspection.

During this process, the master computer 20 continues to monitor thechange in torque and transmits a switching command signal C to the servodriver 16 if the position of the mounting table 11 is adjusted by thetorque change. As illustrated in FIG. 2, the servo driver 16 allows theswitching part 163 to switch the torque control part 162 to the positioncontrol part 161 (step S8). The position of the servo motor 15 iscontrolled to return the mounting table 11 back to a lowermost position.Then, the wafer W is index-moved to bring the next device D to aposition just below the probes 13A (step S9). In this state, the processreturns to step S1 where the servo motor 15 is controlled to bring thedevice D and the probes 13A into contact with each other.

In case of performing the high temperature inspection of the seconddevice D, steps 1 to 5 are repeated in the same manner as set forthabove. The current torque value is compared with the previouslyregistered torque value by means of the comparator 162A. The torque ofthe servo motor 15 is controlled on the basis of the previouslyregistered torque value and the device D is subjected to the hightemperature inspection.

If the thermal expansion of the probe card 13 ceases to exist whilerepeating the inspection, the servo driver 16 is switched to the torquecontrol. This ensures that the torque of the servo motor 15 is notchanged even if the electrode pads Dp of the device D and the probes 13Acome into contact with each other. Therefore, the process proceeds fromstep S6 to step S10 in FIG. 2 and the high temperature inspection of thedevice D is performed while the mounting table 11 is kept in the currentposition. In this inspection, the wafer W remains spaced apart from theprobes 13A during the index-movement of the wafer W. For this reason,the probe card 13 is cooled a little bit by temporarily radiating heat.However, this has little influence on the inspection. Even if theinspection is affected by this, it is possible to perform the inspectionof the wafer W under the predetermined contact load at all times sincethe torque of the servo motor 15 continues to be controlled by the servodriver 16.

With the present embodiment described above, the servo motor 15 is usedas the vertical drive mechanism 12 of the mounting table 11 and thetorque of the servo motor 15 is controlled by the servo driver 16. Thismakes it possible to immediately perform the high temperature inspectionof the wafer W without having to preheat the probe card 13. Eliminationof the preheating time helps greatly shorten the inspection time.Furthermore, it is possible to surely prevent damage of the probe card13 and the wafer W, thereby enabling the inspection to be performed withincreased reliability.

With the present embodiment, the servo driver 16 is connected to themaster computer 20 that monitors the inspection apparatus 10. The mastercomputer 20 includes the position command part 21 for transmitting theposition command signal P to the position control part 161, the torquecommand part 22 for transmitting the torque command signal T1 to thetorque control part 162, and the switching command part 23 fortransmitting the switching command signal C to the switching part 163based on the torque of the servo motor 15. This makes it possible tomonitor the operating state of the vertical drive mechanism 12 at alltimes. Therefore, the high temperature inspection can be performed withincreased reliability by bringing the wafer W placed on the mountingtable 11 into contact with the probes 13A under the predeterminedcontact load at all times.

Furthermore, the servo driver 16 is provided with the storage part 162Dfor storing the torque value indicative of the contact load availableeach time when the high temperature inspection of the device D isperformed. This makes it possible to set the predetermined contact loadin keeping with the expansion of the probe card 13. Moreover, thestorage part 162D is designed to store the upper and lower limit valuesof the predetermined contact load. This eliminates the possibility thatthe device D and the probes 13A make contact with each other under aload falling outside the predetermined contact load, thereby reliablypreventing damage of the device D and the probes 13A. In addition, thetorque control part 162 controls the contact load between the device Dand the probes 13A to become equal to the predetermined contact load inkeeping with the thermal change of the probe card 13. This makes itpossible to perform the inspection under a constant contact load at alltimes even if the probe card 13 undergoes thermal expansion.

The present invention is not limited to the above-described embodimentat all and the constituent elements of the present invention may besuitably changed in design. For example, although the servo motor andthe ball screw are connected by means of the power transmission belt inthe above description, it may be possible to directly connect the servomotor to the ball screw. Furthermore, although the high temperatureinspection of the wafer W is described in the foregoing embodiment, thepresent invention may be equally applied to a low temperature inspectionof the wafer. Moreover, although the wafer is described as an example ofthe target object in the foregoing embodiment, the present invention maybe applied to the inspection of a glass substrate of a liquid crystaldisplay.

The present invention can be applied to an inspection apparatus forinspecting electric characteristics of a target object such as asemiconductor wafer or the like.

What is claimed is:
 1. An inspection method for inspecting electriccharacteristics of a plurality of devices formed on a target object byusing an inspection apparatus which includes a movable mounting tablehaving therein a temperature controller; a vertical drive mechanism forlifting and lowering the mounting table; a control unit for controllingthe vertical drive mechanism; and a probe card having a plurality ofprobes arranged above the mounting table, the vertical drive mechanismincluding an elevation shaft connected to the mounting table and a servomotor for driving the elevation shaft to lift and lower the mountingtable, the inspection method comprising: heating or cooling the targetobject to a predetermined temperature; controlling a position of theservo motor until the target object and the probes come into contactwith each other; and controlling a torque of the servo motor whileinspecting the electric characteristics of the devices after the targetobject and the probes have come into contact with each other, whereinsaid controlling the torque of the servo motor includes adjusting thetorque of the servo motor by lifting or lowering the mounting table whenit is determined that the torque of the servo motor is changed after thetarget object and the probes have come into contact with each other. 2.The inspection method of claim 1, further comprising: storing a torquevalue indicative of a contact load available each time when the electriccharacteristics of the devices are inspected, wherein the stored torquevalue is used for controlling the torque of the servo motor at a nextinspection time.
 3. The inspection method of claim 1, wherein saidcontrolling the torque of the servo motor includes controlling a contactload of the devices and the probes in keeping with thermal deformationof the probe card to become equal to a predetermined contact load. 4.The inspection method of claim 1, wherein said controlling the torque ofthe servo motor includes controlling a contact load of the devices andthe probes to fall within a range between upper and lower limit valuesof a predetermined contact load.
 5. The inspection method of claim 1,wherein said controlling the torque of the servo motor includes stoppingthe servo motor when a contact load of the devices and the probes fallsoutside a range between upper and lower limit values of a predeterminedcontact load.
 6. The inspection method of claim 1, wherein saidcontrolling the torque of the servo motor includes lifting or loweringthe mounting table such that a contact load of the devices and theprobes becomes equal to a predetermined contact load.
 7. The inspectionmethod of claim 1, wherein said controlling the position of the servomotor and said controlling the torque of the servo motor are repeatedfor each inspection time of the devices, wherein, in said controllingthe torque of the servo motor at a first inspection time, whether or notthe torque of the servo motor is changed after the target object and theprobes have come into contact with each other is determined by comparinga current torque of the servo motor at the first inspection time with atorque of the servo motor monitored when the target object and theprobes have come into contact with each other, and wherein, in saidcontrolling the torque of the servo motor at a second or laterinspection time, whether or not the torque of the servo motor is changedafter the target object and the probes have come into contact with eachother is determined by comparing a current torque of the servo motor atthe second or later inspection time with a torque of the servo motoradjusted at a previous inspection time.